Generally, cold-hot storage boxes have a box shaped insulating container having an opening, a lid which is freely opened and closed attached to the edge portion of the opening of this insulating container, and a heat exchange apparatus which is attached to at least one of the lid and the insulating container. These insulating container and lid are manufactured using an insulating material. In some cases, as the aforementioned heat exchange apparatus, an electric cooling element, such as a Peltier element, is used. In this Peltier element, heat generation or absorption occurs at contact points by means of connecting different types of conductors or semiconductors and running a direct electric current; one conductor or semiconductor cools, and the other different conductor or semiconductor warms. This is believed to be a phenomenon that occurs because the ratio of the heat flow and electric flow carried by free electrons is not equal on both sides of the conductor or semiconductor. In addition, if the direction of the flow of the direct electric current is reversed, heat generation and absorption become reversed. To improve the temperature maintaining ability of this kind of cold-hot storage box, not only are improvements necessary in the heat exchange ability of the Peltier element, but improvements in the insulating ability of the insulating material are also necessary.
In addition, ordinary refrigerators comprise an insulating container, piping arranged inside this insulating container, a refrigerant gas which flows in this piping, a gas liquefying means for liquefying this refrigerant gas, and a vaporizer for vaporizing this refrigerant gas. In this refrigerator, a refrigerant gas, such as Freon or the like, is condensed or compressed and liquefied by the gas liquefying means; subsequently, the refrigerant gas absorbs the heat of vaporization from inside the insulating container by means of vaporization by the vaporizer, and the inside of the insulating container is cooled. This kind of refrigerator insulating container uses insulation materials.
However, in the insulation materials used by these insulating containers, because foam materials, such as foam urethane, foam styrene, or the like, are used, it is necessary for the thickness of the insulation to be thickly formed so that the insulation has sufficient insulating ability. In particular, when using foam urethane as insulating material, at production time, in order to completely fill the insulation layer with the insulation material, considerable thickness and pressure are needed; thin insulation layers of several millimeters are difficult to manufacture. The ratio between the capacity of the exterior and the storage capacity (inner capacity), in other words, the volumetric capacity, for the resulting insulating container, has the problem that it is low.
In addition, at the time of manufacture of the insulating container, if the foaming does not happen with sufficient control of the pressure, quantity of foam material, etc., the foam urethane does not spread completely, places of inferior insulation arise, and there is the risk that the insulating ability will be reduced. Furthermore, in some cases, Freon, which causes damage to the ozone layer, is used as a foaming material, and this is not desirable from the point of view of the environment.
On the other hand, in some cases, vacuum insulation is used to improve the insulating ability of the insulating material. In this vacuum insulation, the insulating ability of the insulation material is improved, but production costs become high. Furthermore, in the case of vacuum insulation, a sufficient bearing strength is necessary in the insulating container as the load of atmospheric pressure bears upon the insulating container, and there is a problem with limitations on the shape of the insulating container so that the bearing strength can be obtained.